Solid-state image pickup element and driving method thereof, and camera system

ABSTRACT

In a case where a thinning operation is implemented at the point when signal charges are read out from each of pixels to thin out pixel information by lines (row), the thinning may be performed only in the vertical direction, but not in the horizontal direction. In an all-pixel-read-out type CCD image pickup element, a discharge controlling section is provided in each of VH transfer stage sections transferring signal charges from vertical CCDs to a horizontal CCD, and where a thinning mode is selected, among those signal charges transferred from a plurality of the vertical CCDs, those of a given set of columns are stopped and discharged at the respective discharge controlling sections, and those of the rest of columns are transferred to the horizontal CCD, and at the same time, those of a given set of lines (rows) are stopped and discharged for all columns, thereby performing the thinning operation over the pixel information in both the vertical and horizontal directions at the VH transfer stage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state image pickup element anda driving method thereof, and a camera system, and more specifically toa solid-state image pickup element capable of capturing both stillimages and dynamic picture images and a driving method of the same aswell as to a camera system using the same.

2. Description of the Related Art

A digital still camera (DSC) uses, as its image pickup device, asolid-state image pickup element, such as a charge coupled device (CCD),implementing so-called all-pixel-read-out mode, in which the signalcharges of all pixels are simultaneously read out to a vertical transfersection, and are transferred and outputted individually without beingmixed in the vertical transfer section. For those CCD image pickupdevices intended for the use in DSCs, efforts have been made to increasethe number of pixels in an attempt to improve the capability ofcapturing still images in better quality.

In a case of a digital still camera, means must be provided to allowmonitoring an image being captured in order to adjust the focus or theangle of the camera during picture taking. Accordingly, a digital stillcamera is generally equipped with a monitor to display a captured image,such as a liquid crystal display. Also, it is designed to be capable ofselectively implementing a monitoring mode besides the still image modefor capturing a still image. In order to be able to display an imagecaptured by, especially, a high-pixel-count CCD image pickup element onthe liquid crystal display while in this monitoring mode, it isnecessary to increase the frame rate.

In a digital still camera using, as its image pickup device, ahigh-pixel-count CCD image pickup element implementing theall-pixel-read-out mode, a thinning technique has hitherto been used asone approach for increasing the frame rate in the monitoring mode. Thisthinning technique, as implemented in a CCD image pickup element,provides thinned pixel information by reading out only the signalcharges of pixels in a subset of lines (rows) to the vertical transfersection, and leaving the rest of the lines unread. This thinningtechnique provides a reduction in the amount of data in the verticaldirection, so that the frame rate can be increased.

When attention is directed to those pixels in the lines (rows) to bethinned out in such a CCD image pickup element capable of implementingthe thinning operation, while these pixels are subject to the thinningduring the monitoring mode, they are read out in no different manner asthose pixels of other lines during the normal still image mode, so thatthe driving pattern of those rows to be thinned out is different in themonitoring mode and in the still image mode.

Accordingly, in a conventional CCD image pickup element capable ofimplementing the thinning operation, two driving systems (driving pulse,driving terminals, wirings, etc.) for the regular lines from which thesignal charges are read out, and for those lines from which the signalcharges are not read out (rows to be thinned out) are necessary, and inaddition, the driving systems once configured cannot be modified lateras they are hardwired, so that this approach can provide only apredetermined thinning rate. In other words, one cannot arbitrarilyselect the vertical compressibility.

In addition, the conventional thinning technique involves the thinningoperation of pixel information performed on a row-by-row basis at thepoint where signal charges are read out from the respective pixels, sothat it may provide pixel information thinned in the vertical direction,but not in the horizontal direction. This means that, in the horizontaldirection, the signal charges of all the pixels would be read out.Accordingly, when the pixel count is increased as a result of theefforts to enhance the performance of high-pixel-count CCD image pickupelements, the horizontal transfer section would have to be driven at ahigher rate, and resulting in an increased driving frequency, thus,increased power consumption.

Moreover, in a case where the thinning operation is implemented at thepoint when the signal charges are read out from the sensor section asexplained above, smears and dark currents are generated also in thosethinned out transfer stages of the vertical transfer section in the samemanner as the other transfer stages in which signal charges are presenteven though they have no signal charges so that these smears and darkcurrents are eventually added to the signal charges in the horizontaltransfer section, and the proportion of smear and dark currentcomponents relative to the signal component per pixel is increased,resulting in deterioration in the image quality.

SUMMARY OF THE INVENTION

An object of the present invention, which has been made in considerationwith the above problems, is to provide a solid-state image pickupelement capable of reducing the smear and dark current components andobtaining pixel information that is thinned in both the vertical andhorizontal directions, and also to provide a driving method of the sameas well as a camera system using the same.

In order to achieve the above object, a solid-state image pickup elementaccording to the present invention comprises a plurality of sensorsections arranged in a matrix of rows and columns for performingphotoelectric conversion; a first charge transfer section fortransferring signal charges read out from the plurality of sensorsections in a direction in which the rows are arranged; and a secondcharge transfer section for transferring the signal charges transferredfrom the first charge transfer section in a direction in which thecolumns are arranged, wherein, at the transfer stages transferringsignal charges from the first charge transfer section to the secondcharge transfer section, the transfer of signal charges from a given setof columns is selectively stopped, and these signal charges aredischarged on a column-by-column basis, and the transfer of signalcharges from the other columns is selectively stopped, and these signalcharges are discharged on a row-by-row basis The solid-state imagepickup element having the above configuration is used as the imagepickup device for a camera system.

In a solid-state image pickup element having the above configuration, aswell as in a camera system using such a device as its image pickupdevice, even though the thinning operation over pixel information is notimplemented at the point when signal charges are read out from each ofthe sensor sections, thinning may be performed not only by rows(thinning in the vertical direction), but also by columns (thinning inthe horizontal direction) by selectively discharging signal charges froma given set of columns on a column-by-column basis, and signal chargesof the other columns on a row-by-row basis during the course of thesignal charge transfer from the first charge transfer section to thesecond charge transfer section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an all-pixel-read-out type CCD imagepickup element according to a first embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view of the device in FIG. 1 takenalong the line X-X′, illustrating an exemplary configuration ofdischarge controlling section of a CCD image pickup element according tothe present invention;

FIG. 3 is a timing chart of the thinning mode;

FIG. 4 is an illustrative diagram showing the operation during thethinning mode; and

FIG. 5 is a block diagram showing an exemplary configuration of a camerasystem according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be explained in greaterdetail with reference to the attached figures. FIG. 1 is a schematicdiagram of an all-pixel-read-out type CCD image pickup element accordingto a first embodiment of the present invention. The all-pixel-read-outtype CCD image pickup element according to the present embodiment isexplained herein as being capable of operating in the thinning mode forproviding pixel information thinned in both the vertical (rowarrangement) and horizontal (column arrangement) directions, as well asin the all-pixel-read-out mode.

In the configuration shown in FIG. 1, an imaging area 11 comprises aplurality of sensor sections (pixels) 12 arranged in a matrix of rowsand columns over a semiconductor substrate (not shown), a plurality ofvertical CCDs 13 each provided along the column direction of the pixelsfor every vertical column of the sensor sections 12, and readout gatesections 14 provided between the respective sensor sections 12 and thecorresponding CCDs 13 for reading out signal charges from the sensorsections 12 to the vertical CCDs 13.

In this imaging area 11, each of the sensor sections 12 is constitutedby a photo diode such as a PN junction, and is configured to convertincident light into a corresponding amount of signal charges. Eachvertical CCD 13 is driven by, for example, four-phase vertical transferpulses Vφ1 through Vφ4, and transfers signal charges read out from eachsensor section 12 via the readout gate 14 in the vertical directionsequentially on a row-by-row basis without mixing them (hereinafter,this operation is referred to as a “line shift”).

Provided at the bottom part of the imaging area 11, i.e., thedestination side of the signal charges transferred by the vertical CCDs13, is a horizontal CCD 15 for transferring the signal chargessequentially line-shifted by the vertical CCDS 13, in the horizontaldirection. The horizontal CCD 15 is driven by, for example, two-phasehorizontal pulses Hφ1 and Hφ2. Provided at the end of the transferdestination from the horizontal CCD-15 is a charge/voltage convertersection 16 constituted by, for example, a floating diffusion amplifier.

Provided in a VH transfer stage section located between the plurality ofvertical CCDs 13 and horizontal CCD 15, are discharge controllingsections 17 for selectively stopping the transfer of, and dischargingthe signal charges from a given set of columns on a row-by-row basis,and the signal charges from the remaining set of the columns on acolumn-by-column basis. These discharge controlling sections 17 performthe thinning operation over pixel information in both the vertical andhorizontal directions through providing selective control pulses Gφ1 andGφ2. The configuration of these sections will later be described ingreater detail.

A timing generator (TG) 18 generates various timing pulses for drivingthe CCD image pickup element, including the four-phase vertical transferpulses Vφ1 through Vφ4 for driving the vertical CCDs 13, two-phasehorizontal transfer pulses Hφ1 and Hφ2 for driving the horizontal CCD15, and the two gate control pulses Gφ1 and Gφ2 for driving thedischarge controlling sections 17. This timing generator 18, togetherwith a driver (not shown), etc., constitutes a driving system of the CCDimage pickup element of the above configuration, and sends out thevarious timing pulses to various driving sections via the driver.

In the timing generator 18, especially the four-phase vertical transferpulses Vφ1 through Vφ4, the two-phase horizontal transfer pulses Hφ1 andHφ2, and the two gate control pulses Gφ1 and Gφ2 are generated at thetimings adequate for the respective operating modes (normalmode/thinning mode) based on externally-supplied mode information.

FIG. 2 is a schematic cross-sectional view of the device in FIG. 1 takenalong the line X-X′, showing an exemplary configuration of the dischargecontrolling section 17.

With reference to FIG. 2, over, for example, an N-type semiconductorsubstrate 21, a transfer channel 23 (in the figure, indicated as 23-1through 23-4) for transferring signal charges in the vertical direction(orthogonal direction relative to the surface of the paper) is formed byan N-type impurity via a P-well 22 on the top surface side of the P-well22. This transfer channel 23, together with the transfer electrode (forexample, a double-layer electrode structure) 24 provided thereon, formsa vertical CCD 13 (in the figure, indicated as 13-1 through 13-4).

In the region between two vertical CCDS, for example, in the centerregion between the leftmost vertical CCD 13-1 and the second verticalCCD 13-2 from the left, a drain section 25-1 is formed by an N⁺-typeimpurity on the surface side of the substrate. This drain section 25-1is in contact with an Al (aluminum) wire 26-1, and is biased by a givendrain voltage Vd applied externally via this Al wire 26-1.

Between this drain section 25-1 and the two transfer channels 23-1 and23-2 on its both sides, embedded channels 27-1 and 27-2 are formed.These embedded channels 27-1 and 27-2 are formed in the same profile asthe transfer channels 23 (23-1 through 23-4) of the vertical CCDs 13, inother words, they are formed with the same N-type impurity, and theseembedded channels and gate electrodes 28-1 and 98-2 thereon, formedindependently from the transfer electrodes 24 of the vertical CCDs 13,constitute discharging gate sections 29-1 and 29-2 for selectivelydischarging signal charges from the transfer channels 23-1 and 23-2 intothe drain section 25-1.

In these discharging gate sections 29-1 and 29-2, either of theaforementioned gate control pulses Gφ1 and Gφ2 is applied to the gateelectrodes 28-1 and 28-2. Accordingly, the gate electrodes to which thedifferent gate control pulses are applied are formed as electrodes ofseparate layers made of, for example, polysilicon or a metal(double-layer electrode structure).

In the case of the present embodiment, as shown in FIG. 2, the gatecontrol pulse Gφ1 is applied to the leftmost gate electrode 29-1, andthe gate control pulse Gφ2 is applied to the second, third and fourthgate electrodes 29-2, 29-3 and 29-4 from the left. For the rest of thegate electrodes from the fifth and later, the same pulse-applicationpattern of the first through fourth gate electrodes 29-1 through 29-4 isrepeated for every four gate electrodes.

In the present embodiment, the discharge controlling section 17 isexplained as providing one drain section 25-1, 25-2 . . . . . . forevery two columns (two vertical CCDS), however, it may alternatively beconfigured to provide one drain section for every single column.

Next, the operations of the CCD image pickup element having the aboveconfiguration for the respective modes (normal mode/thinning mode) willnow be explained. During the readout process of signal charges from thesensor sections (pixels) 12, the signal charges of all the pixels aresimultaneously read out to the vertical CCDs 13 regardless of theoperating mode.

In the normal mode, all signal charges read out to the vertical CCDs 13must be sequentially line-shifted into the horizontal CCD 15, so thatthe timing generator 18 supplies the low-level control pulses Gφ1 andGφ2 to the discharge controlling sections 17.

These low-level gate control pulses Gφ1 and Gφ2 are applied to each ofthe gate electrodes 28-1, 28-2 . . . . . . of the discharging gatesection 29-1, 29-2, . . . . . . shown in FIG. 2. Upon this, each of theembedded channels 27-1, 27-2 . . . . . . of the discharging gatesections 29-1, 29-2, . . . . . . would turn into a shallow potentialstate, so that the signal charges in the vertical CCDs 13 would passthrough the VH transfer stage section and reach to the horizontal CCD15, and they would not flow into the drain sections 25-1, 25-2, . . . .. .

Therefore, while in the normal mode, all the signal charges read out tothe vertical CCDs 13 are sequentially line-shifted on a row-by-row basisto the horizontal CCD 15 through the transfer behavior of the verticalCCDs 13, whereas the signal charges of every single row that have beenline-shifted to the horizontal CCD 15 are horizontally transferredsequentially through the transfer behavior of the horizontal CCD 15, andare converted into signal voltages at the charge/voltage convertersection 16, and then outputted.

Then, the operation of the thinning mode will now be explained withreference to the timing chart of FIG. 3 and the diagram of FIG. 4illustrating the operation. The thinning operation performed in thisembodiment is explained on the discharge controlling section 17, asbeing configured for thinning out three lines (rows) from every fourlines (rows) in the vertical direction, and three columns from everyfour columns in the horizontal direction.

During the thinning operation in the present embodiment, the four-phasevertical transfer pulses Vφ1 through Vφ4, the two-phase horizontaltransfer pulses Hφ1 and Hφ2, and the gate control pulses Gφ1 and Gφ2,having a relative timing relationship shown in FIG. 3, are outputtedfrom the timing generator 18. In the illustrative diagram of FIG. 4, thesymbols “o” represent signal charges to be eventually read out, and thesymbols “•” represent signal charges to be thinned out.

At the point where the signal charges of all the pixels aresimultaneously read out from the sensor sections 12 to the vertical CCDs13, first, the signal charges of those pixels in the first line (row)would be line-shifted through the vertical transfer behavior of thevertical CCDs 13 driven by the four-phase vertical transfer pulses Vφ1through Vφ4. At this point, the gate control pulse Gφ1 is in a low-levelstate, and the gate control pulse Gφ2 is in a high-level state.

Accordingly, each of the embedded channels 27-1, 27-5 . . . . . . of thedischarging gate sections 29-1, 29-5 . . . . . . on the side of thevertical CCDs 13 at the first, fifth . . . . . . columns would be turnedinto a shallow-potential state, so that the signal charges within thosevertical CCDs 13 at the first, fifth . . . . . . columns would passthrough the VH transfer stage section to reach to the horizontal CCD 15as shown in FIG. 4A.

On the other hand, in the discharging gate sections 29-2, 29-3, 29-4 . .. . . . of the remaining vertical CCDs 13, each of the embedded channels27-2, 27-3, 27-4, . . . . . . would turn into a deep-potential state, sothat the signal charges in those remaining vertical CCDs 13 would bedischarged to the respective drain sections (indicated as “D” in thefigure) via the gate sections 29-2, 29-3, 29-4, . . . . . . .

As a result, among the signal charges of the first line (row), onlythose in the first, fifth, . . . . . . columns would be transferred tothe horizontal CCD 15, and those in the rest of the columns are stoppedat the discharge controlling sections 17 and discharged into the drainsections 25-1, 25-2 . . . . . . , so that thinned signal charges areobtained. The subsequent signal charges in the following three lines(rows) from the second through the fourth, are thinned out on aline-by-line basis at the respective discharge controlling sections 17.

More specifically, at the time of the line-shifting operation for thesignal charges in these three lines (second through fourth lines), boththe gate control pulses Gφ1 and Gφ2 are turned into a high-level state.Accordingly, as shown in FIG. 4B, the signal charges of the three linesfrom the second through fourth would be stopped at the dischargecontrolling sections 17 and discharged into the respective drainsections 25-1, 25-2 . . . . . . to be thinned out by every line-shiftingbehavior.

While the thinning operation is performed for the signal charges inthese three lines, a 1-bit shift is performed in the horizontal CCD 15to transfer the signal charges by 1 bit (by one transfer stage) as shownin FIG. 4B. The signal charges of the fifth line are line-shifted in amanner shown in FIG. 4C.

This line shift of the fifth line is performed in the same manner as theline shift of the first line. As a result, among the signal charges ofthe fifth line, only the signal charges in the first, fifth . . . . . .columns are transferred to the horizontal CCD 15, and the signal chargesin the rest of the columns are stopped at the discharge controllingsections 17 and discharged into the drain sections 25-1, 25-2 . . . . .. to be thinned out.

The signal charges of the following three lines from the sixth througheighth lines are thinned out on a line-by-line basis in the same manneras the three lines from the second through fourth lines. Thereafter, thethinning by columns and by rows in the discharge controlling sections17, and the 1-bit shift in the horizontal CCD 15 are repeated until allthe packets (all transfer stages) of the horizontal CCD 15 are occupiedwith the signal charges.

In the present embodiment, this operation is implemented for thinningout three lines of pixel data from every four lines in the verticaldirection, and three columns of pixel data from every four columns inthe horizontal direction, so that a series of the aforementioned stepsare performed for every 16 lines. When the line-shifting steps arecompleted for the signal charges of 16 lines, and all the packets of thehorizontal CCD 15 are occupied by the signal charges, the signal chargesare sequentially transferred to the charge/voltage converter section 16through the horizontal transfer behavior of the horizontal CCD 15 drivenby the two-phase horizontal transfer pulses Hφ1 and Hφ2 as shown in FIG.4D.

The charge/voltage converter section 16 converts the signal charges thatare sequentially transferred on a pixel-by-pixel basis from thehorizontal CCD 15 into signal voltages that are then outputted. At thispoint, the CCD output in the thinning mode would represent a signal inwhich a pixel signal derived from the 4 lines within the unit of 16lines is repeated in a 4-pixel cycle. Accordingly, when the thinningmode is selected, a recovering process would have to be performed by asignal processing circuit located in the later stage for recovering aline-by-line signal that corresponds to the original pixel arrangementfrom that CCD output signal.

In the above description of the operation, the operation has beenexplained as being configured to thin out three lines (rows) of pixeldata from every four lines in the vertical direction, and three columnsof pixel data from every four columns in the horizontal direction.However, it should be understood that any other combination may also beused. That is, in the case of the vertical thinning operation, thethinning rate in the vertical direction may be arbitrarily determined byselecting the generation timing of the low-level gate control pulse Gφ1shown in FIG. 3, which is the pulse to select lines to be transferred.

On the other hand, in FIGS. 1 and 2, the thinning rate in the horizontaldirection may be controlled by selectively specifying the gateelectrodes 28-1, 28-2 . . . . . . of the discharging gate sections 29-1,29-2 . . . . . . to which the gate control pulse Gφ2 (the pulse toselect the columns to be thinned out) is applied.

In this case, the thinning rate once designed would have to be hardwiredsince the gate control pulse Gφ2 is applied to the gate electrodes 28-1,28-2 . . . . . . through patterned wirings. However, it is possible toallow the thinning rate in the horizontal direction to be arbitrarilyset with a limited freedom by providing in advance several patternedwirings corresponding to several thinning rates, and using aconfiguration that allows the selection of either one of these patternedwirings to be used for applying the gate control pulse Gφ2.

Furthermore, in the above description of the operation, the horizontaltransfer is explained as being conducted only after all the packets ofthe horizontal CCD 15 are filled with signal charges of a plurality oflines during the horizontal thinning, however, the horizontal transferof the signal charges of the plurality of lines may also be conductedover several times. In this case, however, the horizontal transfer ispreferably conducted after at least two lines (rows) of signal chargesare line-shifted to the horizontal CCD 15 when the consideration isgiven to the reduction in the power-consumption of the CCD image pickupelement as described later.

As explained above, in the all-pixel-read-out type CCD image pickupelement, discharge controlling sections 17 are provided in the VHtransfer stage section, and when the thinning mode is selected, amongthose signal charges transferred from the plurality of vertical CCDs 13,those from a given set of columns are stopped and discharged, and thosefrom the rest of the columns are transferred to the horizontal CCD 15and also, those of a given set of lines are stopped and discharged forall the columns, thereby obtaining pixel information thinned at the VHtransfer stage section in both the vertical and horizontal directions.

Since pixel information may be thinned also in the horizontal directionat the VH transfer stage in this manner to reduce the amount of signalcharges to be horizontally transferred by the horizontal CCD 15, thedriving frequency of the horizontal CCD 15, that is, the frequency ofthe horizontal transfer pulses Hφ1 and Hφ2, may be reduced by thatextent. For instance, considering a case where pixel information ofthree pixels is thinned out from each unit of four pixels in thehorizontal direction, by conducting a horizontal transfer after signalcharges of four lines are line-shifted to the horizontal CCD 15 (eachinvolving a 1-bit shift), the driving frequency may be reduced to ¼ of acase in which every single line of the signal charges from all pixelsare horizontally transferred. As a result, the power consumption of theCCD image pickup element may be reduced.

In the case of the vertical thinning, since the thinning operation isimplemented in the VH transfer stage, not at the point where signalcharges are read out from the sensor sections 12, those smear and darkcurrent components, generated within the vertical CCDs 13 in associationwith the thinned-out pixels, may also be discharged along with thesignal charges at the discharge controlling sections 17, so that it hasan advantage in that the smear and dark current components may bereduced relative to a case in which the vertical thinning is conductedat the point where the signal charges are read out from the sensorsections 12.

It should be noted that, in the discharge controlling section 17, sincethe embedded channels 27-1, 27-2 . . . . . . of the discharging gatesections 29-1, 29-2 . . . . . . are formed in the same profile as thetransfer channels 23-1, 23-2 . . . . . . of the vertical CCDs 13-1, 13-2. . . . . . , there would be no difference in the potential levelbetween them and the transfer channels 23-1, 23-2, . . . . . . when thetransfer channels are in a deep potential state, so that smear and darkcurrent components can be completely discharged from the transferchannels 23-1, 23-2, . . . . . . .

FIG. 5 is a block diagram showing an exemplary configuration of a camerasystem using a CCD image pickup element of the above configurationaccording to the present invention.

Referring to FIG. 5, the camera system according to the presentinvention comprises a CCD image pickup element 31 which serves as theimage pickup device of the system, a lens 32 for collecting and formingan image of incident light (image light) from an object onto an imagepickup surface of this CCD image processing CCD output signals from theCCD image pickup element 31, an image storage device 34 for storing theoutput signals from the signal processing circuit 33 in a storagemedium, an image display device 35 for displaying the output signals ofthe signal processing circuit 33 on a monitoring display, a timingcontroller 36 for providing timing control for the whole system, and amode setting section 37 for setting the image capturing mode of the CCDimage pickup element 31.

Used herein as the CCD image pickup element of the camera system of theabove configuration is a CCD image pickup element having theconfiguration priorly described, that is, the CCD image pickup element31 capable of performing the thinning operation in both the vertical andhorizontal directions in its VH transfer stage section. The mode settingsection 37 accordingly sets the image capturing mode for this CCD imagepickup element 31, either to a still image mode for capturing a stillimage or to a monitoring mode for monitoring an object to be captured(dynamic picture image mode). Herein, the “still image mode” correspondsto the “normal mode”, and the “monitoring mode” corresponds to the“thinning mode” of the aforementioned CCD image pickup element,respectively.

In the aforementioned CCD image pickup element (see FIG. 1), the timinggenerator 18 generates various timing pulses such as the four-phasevertical transfer pulses Vφ1 through Vφ4, two-phase horizontal transferpulses Hφ1 and Hφ2, and two gate control pulses Gφ1 and Gφ2, having therelative timing relationship shown in FIG. 3, when the monitoring mode(thinning mode) is selected through the mode setting section 37.

In this way, while in the thinning mode, the thinning operation isperformed to thin out three lines (rows) of the pixel information fromevery four lines in the vertical direction, and three columns of thepixel information from every four columns in the horizontal direction inthe VH transfer stage of the CCD image pickup element. Also in thismonitoring mode (thinning mode), the thinning rate (compression rate)may also be controlled from a control panel (not shown) which alsoincludes the mode setting section 37.

The image storage device 34 stores image signals processed by the signalprocessing circuit 33 into a storage medium such as a memory or a floppydisk when the still image mode is selected through the mode settingsection 37. The pixel information stored in this storage medium can bereproduced as a hard copy using a printer, etc. The image display device35 displays the image signals processed by the signal processing circuit33 on a monitoring display such as a CRT (cathode-ray tube) or an LCD(liquid crystal display) as a dynamic picture image when the monitoringmode is selected through the mode setting section 37.

By the use of the CCD image pickup element according to the presentinvention as the image pickup device of a camera system such as adigital still camera, one would be able to monitor a dynamic pictureimage at a higher image quality with arbitrary compression rates in boththe vertical and horizontal directions in the monitoring mode (dynamicpicture image mode). Moreover, the ability to minimize the drivingfrequency in the horizontal direction in the monitoring mode (thinningmode) would reduce the power consumption of the CCD image pickupelement, so that batteries would last longer.

As explained heretofore, according to the present invention, in asolid-state image pickup element and in a camera system using the sameas its image pickup device, signal charges of a given sets of columnsare selectively stopped and discharged on a column-by-column basis, andsignal charges of the rest of columns are selectively stopped anddischarged on a row-by-row basis at the transfer stage sectiontransferring signal charges from the first charge transfer section tothe second charge transfer section, so that even though the thinningoperation is not implemented at the point where the signal charges areread out from each of the sensor sections, the thinning by rows.Furthermore, since any smear and dark current components may also bedischarged at the aforementioned transfer stage sections, the quality ofan image may be improved.

1. A solid-state image pickup element comprising: a plurality of sensorsections arranged in a matrix of rows and columns for performingphotoelectric conversion; a first charge transfer section fortransferring signal charges read out from said plurality of sensorsections in a direction in which the rows are arranged; a second chargetransfer section for transferring the signal charges transferred fromsaid first charge transfer section in a direction in which the columnsare arranged; and a discharge controlling section provided in a transferstage which transfers the signal charges from said first charge transfersection to the second charge transfer section, said dischargecontrolling section stopping the transfer of, and instead discharging,the signal charges of a given set of columns selectively on acolumn-by-column basis, and those signal charges of the remainingcolumns selectively on a row-by-row basis, wherein said dischargecontrolling section comprises a drain section, a transfer channel, and adischarging gate section provided between said transfer channel and saiddrain section for selectively discharging the signal charges from saidtransfer channel into said drain section, and wherein said discharginggate section comprises an embedded channel, formed in the same profileas said transfer channel, and a gate electrode disposed over saidembedded channel.
 2. (canceled)
 3. (canceled)
 4. A driving method of asolid-state image pickup element comprising a plurality of sensorsections arranged in a matrix of rows and columns for performingphotoelectric conversion, a first charge transfer section fortransferring signal charges read out from said sensor sections in adirection in which the rows are arranged, and a second charge transfersection for transferring the signal charges transferred from said firstcharge transfer section in a direction in which the columns arearranged, said method comprising a step of: stopping the transfer of,and instead discharging, those signal charges of a given set of columnsselectively on a column-by-column basis, and signal charges of theremaining columns selectively on a row-by-row basis by selectivelyapplying control signals to a gate electrode formed over an embeddedchannel.
 5. The driving method of a solid-state image pickup element asclaimed in claim 4, wherein the three steps of: 1) transferring signalcharges of a given row to said second charge transfer section; 2)driving said second charge transfer section to perform a transfer by onetransfer stage; and 3) driving said first charge transfer section totransfer signal charges of a subsequent row to be transferred, to saidsecond charge transfer section; are repeated until the signal charges oftwo rows or more are accommodated in said second charge transfersection; and thereafter performing a step of driving said second chargetransfer section to transfer and output all the signal charges.
 6. Acamera system comprising: a solid-state image pickup element having aplurality of sensors arranged in a matrix of rows and columns, a firstcharge transfer section for transferring signal charges read out fromsaid plurality of sensor sections vertically, a second charge transfersection for transferring the signal charges transferred from said firstcharge transfer section horizontally, and a discharge controllingsection provided to transfer the signal charges from said first chargetransfer section to the second charge transfer section, said dischargecontrolling section serving to discharge instead of transferring, thosesignal charges of a given set of columns selectively on acolumn-by-column basis, and those signal charges of any remainingcolumns selectively on a row-by-row basis; wherein said dischargecontrolling section comprises a drain, a transfer channel, and adischarging gate provided between said transfer channel and said drainfor selectively discharging the signal charges from said transferchannel into said drain, and wherein said discharging gate comprises anembedded channel, formed in a same profile as said transfer channel, anda gate electrode disposed over said embedded channel; said systemfurther comprising: a mode setting means allowing an alternativeselection between a first mode and a second mode; and driving meanswhich does not drive said discharge controlling section to perform thedischarging operation of signal charges when said first mode has beenselected through said mode setting means, and which does drive saiddischarge controlling section to perform the discharging operation whenthe second mode has been selected through said mode setting means.
 7. Asolid-state image pickup element comprising: a plurality of sensorsarranged in a matrix of rows and columns for performing photoelectricconversion; a first charge transfer section for transferring signalcharges read out from said plurality of sensors vertically; a secondcharge transfer section for transferring the signal charges transferredfrom said first charge transfer section horizontally; and a dischargecontrolling section which transfers the signal charges from said firstcharge transfer section to the second charge transfer section, saiddischarge controlling section comprises a drain offset from a transferchannel and a discharging gate provided between said transfer channeland said drain, said discharging gate comprises a buried channel, formedin a same level as said transfer channel, and a gate electrode disposedover said buried channel.
 8. The solid-state image pickup element asclaimed in claim 7, wherein said discharge controlling section stopsdischarges instead of transferring signal charges of a given set ofcolumns selectively on a column-by-column basis, and those signalcharges of remaining columns selectively on a row-by-row basis.